Wavelength division multiplexing transmission system and apparatus and optical signal noise ratio calculation method

Abstract

A wavelength division multiplexing (WDM) transmission system for transmitting a wavelength division multiplexed signal light from a sender transmission apparatus to a receiver transmission apparatus is provided. The system comprises a computing unit that subtracts from a first optical signal noise ratio (OSNR) of the signal light measured by the receiver transmission apparatus a second OSNR ascribed to a sideband of the signal light measured by the sender transmission apparatus so as to compute a corrected OSNR of an amplified spontaneous emission (ASE) noise light with a reduction of an effect of the sideband.

What is claimed is: 
     
       1. A wavelength division multiplexing (WDM) transmission system for transmitting a wavelength division multiplexed signal light from a sender transmission apparatus to a receiver transmission apparatus, the system comprising:
 a first computing unit that subtracts from an originally-measured optical signal to noise ratio (OSNR) of the signal light, which is measured by the receiver transmission apparatus, an additional OSNR ascribed to a harmonic signal sideband of the signal light measured by the sender transmission apparatus so as to compute a corrected OSNR of an amplified spontaneous emission (ASE) noise light with a reduction of an effect of the signal sideband which is considered as noise in the originally-measured OSNR of the signal light. 
 
     
     
       2. The WDM transmission system of  claim 1 , wherein the sender transmission apparatus comprises:
 a wavelength multiplexer that wavelength-multiplexes the signal light; and 
 an optical amplifier that amplifies the signal light wavelength-multiplexed by the wavelength-multiplexer, wherein 
 the sender transmission apparatus measures the additional OSNR from the signal light sampled between the wavelength multiplexer and the optical amplifier and reports the measured additional OSNR to the receiver transmission apparatus. 
 
     
     
       3. The WDM transmission system of  claim 2 , wherein the receiver transmission apparatus comprises a WDM monitor that measures the originally-measured OSNR of the signal light, and
 wherein the WDM monitor subtracts from the originally-measured OSNR the additional OSNR reported by the sender transmission apparatus. 
 
     
     
       4. The WDM transmission system of  claim 1 , wherein the sender transmission apparatus transmits the additional OSNR to the receiver transmission apparatus via a transmission channel for transmitting the signal light. 
     
     
       5. The WDM transmission system of  claim 1 , wherein the receiver transmission apparatus comprises:
 a WDM monitor that measures the originally-measured OSNR of the signal light; and 
 a monitor/control unit that is connected to a communication network, and wherein 
 the monitor/control unit subtracts the additional OSNR, which is reported by the sender transmission apparatus, from the originally-measured OSNR provided by the WDM monitor. 
 
     
     
       6. The WDM transmission system of  claim 5 , wherein the sender transmission apparatus reports the additional OSNR to the receiver transmission apparatus via the communication network. 
     
     
       7. The WDM transmission system of  claim 1 , wherein the sender transmission apparatus comprises:
 a measuring unit, which receives from an optical amplifier an output signal light containing an ASE component and which measures an initial OSNR of the output signal light ; and 
 a second computing unit, which obtains an ASE OSNR corresponding to only the ASE component of the output signal light and which subtracts the ASE OSNR from the initial OSNR of the output signal light so as to compute the additional OSNR. 
 
     
     
       8. The WDM transmission system of  claim 7 , wherein the sender transmission apparatus further comprises:
 a WDM monitor, which measures the initial OSNR of the output signal light that is sampled from an output terminal of the optical amplifier; and 
 a storage unit, which stores the obtained ASE OSNR. 
 
     
     
       9. The WDM transmission system of  claim 8 , wherein the ASE OSNR is measured beforehand and stored in the storage unit at the time of manufacturing the optical amplifier. 
     
     
       10. The WDM transmission system of  claim 8 , wherein the storage unit stores a minimum ASE OSNR component (OSNRmin) and a maximum ASE OSNR component (OSNRmax) that are measured beforehand, the OSNRmin and the OSNRmax being the values of the OSNR of a channel n measured at an output terminal of the optical amplifier when a light source of a wavelength of the channel n is input to the optical amplifier at a minimum input optical power (Pmin) and a maximum input optical power (Pmax), respectively, and
 wherein the sender transmission apparatus uses an optical power value of channel n (Pn) to compute the ASE OSNR, where ASE OSNR =(OSNRmin) +((OSNRmax-OSNRmin)*(Pn-Pmin)) /(Pmax-Pmin), where Pmin <Pn <Pmax. 
 
     
     
       11. An optical signal to noise ratio calculation method employed in a wavelength division multiplexing (WDM) transmission system for transmitting a wavelength division multiplexed signal light from a sender transmission apparatus to a receiver transmission apparatus, the method comprising:
 measuring an original optical signal to noise ratio (OSNR) of the signal light in the receiver transmission apparatus; 
 measuring an additional OSNR ascribed to a harmonic signal sideband of the signal light in the sender transmission apparatus; and 
 subtracting the additional OSNR from the original OSNR so as to compute a corrected OSNR of an amplified spontaneous emission (ASE) noise light with a reduction of an effect of the signal sideband which is considered as noise in the original OSNR of the signal light. 
 
     
     
       12. The optical signal to noise ratio calculation method of  claim 11 , further comprising:
 measuring the additional OSNR from the signal light sampled between a wavelength multiplexer and an optical amplifier in the sender transmission apparatus, with the wavelength multiplexer wavelength-multiplexing the signal light and the optical amplifier amplifying the signal light wavelength-multiplexed by the wavelength-multiplexer; and 
 reporting the additional OSNR that is measured to the receiver transmission apparatus. 
 
     
     
       13. A wavelength division multiplexing (WDM) transmission apparatus for transmitting a wavelength division multiplexed signal light, the WDM transmission apparatus comprising:
 a wavelength multiplexer that wavelength-multiplexes a signal light; 
 an optical amplifier that amplifies the signal light wavelength-multiplexed by the wavelength multiplexer before transmission by the WDM transmission apparatus; 
 an optical branching unit, which branches the signal light between the wavelength multiplexer and the optical amplifier; 
 a WDM monitor, which measures an optical signal to noise ratio of the signal light sampled at the optical branching unit; and 
 a monitor control unit, which reports the optical signal to noise ratio measured by the WDM monitor to a signal light destination, 
 wherein the monitor control unit is notified of a corrected optical signal to noise ratio with a reduction of an effect of a signal sideband considered as noise in the optical signal to noise ratio measured by the WDM transmission apparatus. 
 
     
     
       14. A wavelength division multiplexing (WDM) transmission apparatus for transmitting a wavelength division multiplexed signal light, the WDM transmission apparatus comprising:
 an optical amplifier that amplifies a transmitted signal light; 
 an optical branching unit, which branches the signal light amplified by the optical amplifier; and 
 a WDM monitor, which measures an original optical signal to noise ratio (OSNR) of the signal light sampled at the optical branching unit, wherein 
 the apparatus subtracts from the original OSNR, measured by the WDM monitor, an additional OSNR ascribed to a harmonic signal sideband of the signal light provided from the source of the signal light so as to compute a corrected OSNR of an amplified spontaneous emission (ASE) noise light with a reduction of an effect of the signal sideband which is considered as noise in the original OSNR of the signal light.